YES!
Peacocks CAN become aggressive, despite their reputation to the contrary.
A few years ago a peacock appeared in our neighborhood out of nowhere. I guess somebody abandoned him. He was an adult male.
He lived in the neighborhood for several months without incident, and frankly, everybody kind of liked him strutting his proud little self about. He was the center of attraction at a barbecue I held for some friends. My daughter loved him. The peacock often hung around in 50 foot tall pine trees right near our back yard.
But then came springtime and what I have been told is peacock mating season. I don't know if being mating season affected what happened, but this much I can tell you:
My wife and I are avid organic gardeners, and March is the time to put out the lettuce around here. My wife put out some small romaine lettuce transplants along with some cole crop transplants. The same way she does every year.
But this year, her romaine lettuce was getting eaten to the ground. She didn't know what was eating her romaine, but decided to replant since it was still early in the growing season.
So she went out with some more transplants, and stooped over to plant them. About half way through the re-planting, she heard a horrible, loud sound (she described it as being similar to the horrible sound that Nazi dive bomber planes made as they swooped down over the skies of Europe during WW2).
She was stooped down when the loud noise suddenly came towards her, and straightened up very quickly -- and they missed each other by inches. She thinks she swung her arms at him to keep him off of her, but everything happened so quickly and she was so frightened and startled that she isn't sure. The quick jolt upward, however, caused her blood pressure to dip really bad and she almost lost consciousness because of that.
Turns out, the peacock was the one eating her romaine lettuce plants, and our best guess is that the peacock must have thought that she was eating his lettuce rather than replacing lettuce he had already eaten. I guess when he saw her "go after his private, reserve food stash" he decided to attack her.
Anyway, the law in this area does not protect peacocks and since my wife has dangerously high blood pressure (the garden is SUPPOSED to help relax her and help her work down her blood pressure), the local animal control officer and I didn't feel it was safe to allow the peacock to stay in the area. So the local animal control officer ended up shooting it after trapping did not work.